Protein is a nutrient component essential for, among other things, the formation and maintenance of muscle. It has generally been said that athletes should ingest protein in an amount ranging from 1.5 to 2.0 g/kg body weight per day in order to reinforce the muscles and to enhance their stamina, although the amount varies depending on their age and living environment (RINSHO EIYO (Clinical Nutrients), 1992, Vol. 80, No. 5, pp. 495-502). More specifically, in case of a player whose body weight is 70 kg, it is necessary to take about 120 g of proteins per day. However, if such a large amount of protein is taken as the usual diet, the total amount of the diet is considerably increased. As a result, it would be painful for players to take a meal and he should be in excess training for preventing any accumulation of excess calorie as fats in the body. This may in turn become a cause of damage or shorten the life of the player.
In addition, it is well known and understood that protein is a nutritional requirement for all living things. While non-athletes may not require as high levels of protein in the diet as do athletes, protein from various sources is a necessary part of the diet for all of the earth's population.
For these reasons (and others), protein can be, and sometimes should be, supplemented from a source other than the usual meal, and accordingly, it has been planned to solve the foregoing problem by making use of a protein-supply food having a high protein content. A variety of proteins can be used as those for the protein-supply food, but it is one of the mainstreams to use milk proteins and soybean proteins since they are particularly high quality proteins. In particular, the soybean proteins have become of major interest lately because of their low price.
Moreover, in recent studies (for instance, Federal Register, 64 FR 57699, Oct. 26, 1999 (Food Labeling: Health Claim: Soy Protein and Coronary Heart Disease: Final Rule)), it is reported that a protein intake of 25 g per day would show such effects as the reduction of the cholesterol content and the reduction of any risk of suffering from heart diseases. Therefore, the efficacy of the soybean protein has increasingly attracted the interest of not only athletic sports players, but also healthy persons.
As foods capable of providing such soybean protein, there have been investigated liquid foods such as soybean milk. However, the smell peculiar to the soybean milk sometimes becomes a problem, and these liquid foods also suffer from a problem of storability and portability. For this reason, it has recently become desirable to move from such liquid foods to powdery soybean protein, which can easily be handled.
The powdery soybean protein may directly be ingested, but this is not common since it does not easily pass through the throat. It may likewise be possible to first disperse the powdery soybean protein in a liquid such as water or milk and then drink the resulting dispersion in order to make the intake thereof. However, the powdery soybean protein is in a fine particulate condition and if it is added to a liquid, it suspends on the surface of the liquid to thus form the so-called “DAMA” (lumps or masses). The phenomenon of this “DAMA” cannot easily be eliminated by simply stirring with, for instance, a spoon. In other words, it is impossible to make the powdery soybean protein drinkable simply by introducing it into a liquid and then subjecting the mixture to simple stirring. Moreover, it is possible to convert the powdery soybean protein into a condition approximately similar to a drinkable liquid by intensively stirring such a mixture using a high speed-stirring machine such as a homogenizer, but this method is not generally performed. Even if the powdery soybean protein is forced to disperse in a liquid using such a method, the resulting dispersion is improved in the palatability and the ability to pass through the throat, but such problems as the smell peculiar to the soybean, a bitter taste thereof, a harsh taste and astringency are not solved. Therefore, people are often reluctant to drink such dispersions.
Conventionally, powdery soybean protein has been prepared by spray-drying an aqueous solution of soybean protein per se, or after adding lecithin to the aqueous solution. However, the soybean protein products prepared according to these methods still suffer from the foregoing problems.
Other various methods for preparing powdery soybean protein products have been reported, but none of them solve all of the foregoing problems. For instance, Japanese Un-Examined Patent Publication No. Hei 8-131083 discloses soybean protein powder prepared by blending or mixing an aqueous solution containing soybean protein for preparing solidified soybean protein foods such as bean curd with a polyglycerin fatty acid ester comprising a fatty acid having 8 to 18 carbon atoms and a polyglycerin having a degree of polymerization ranging from 4 to 10, and then drying the resulting mixture. In the foregoing method for preparing soybean protein powder, a synthetic surfactant is used instead of lecithin, which is a naturally occurring surfactant conventionally used to improve the dispersibility of the soybean protein. This method would permit the improvement of the dispersibility, but does not address taste and/or palatability issues. In addition, Japanese Un-Examined Patent Publication No. Hei 8-131083 also discloses that the dried soybean protein powder may be granulated or formed into granules while using a binder such as sucrose, lactose, trehalose, dextrin or carboxymethyl cellulose. Such granulation would permit the improvement of the dispersibility in, for instance, water. However, this procedure cannot solve all of the problems concerning the smell, bitter taste, harsh taste and astringency peculiar to the soybean.
Furthermore, Japanese Un-Examined Patent Publication No. Hei 9-275911 discloses a powdery soybean protein product prepared by adding 2 to 40 parts by weight of starch hydrolyzate having a DE of 5 to 30 per 100 parts by weight of the solid content of an aqueous solution containing soybean protein components and then drying the resulting mixture. In this invention, the starch hydrolyzate having a DE of 5 to 30 is dispersed throughout the particles to thus improve the dispersibility of the soybean protein components in a liquid. However, if the added amount of the starch hydrolyzate is insufficient, it takes a long period of time to completely disperse the soybean protein components in a liquid. On the other hand, if the added amount of the starch hydrolyzate is increased to ensure rapid dispersion thereof, the concentration of the soybean protein is reduced. Moreover, this method shows an effect of masking, for instance, the smell of soybean in the liquid to some extent, but it is insufficient in the effect of improving astringency and rough feeling of the product.
In addition, Japanese Un-Examined Patent Publication No. Hei 8-154593 proposes a method for preparing a soybean protein material comprising the steps of hydrolyzing an aqueous system containing soybean protein to a rate of hydrolyzing ranging from 5 to 20, adding 5 to 50 parts by weight of fats and oils to 100 parts by weight of the soybean protein before or after the hydrolysis to form an emulsion, preferably dispersing an emulsifying agent, and drying the resulting emulsion. In this example, the decomposition of the protein and the addition of fats and oils permits the improvement of the dispersibility and taste and texture and the resulting product is suitable for use in making concentrated liquid such as soup and pickle liquids. However, if fats and oils are added in such an amount that the smell, bitterness, harsh taste and astringency are replaced with the taste and texture of the fats and oils, the content of protein is reduced and therefore, the product is unfavorable as a protein-supply food.
Furthermore, there has been proposed a method for the preparation of powdery soybean protein, which makes use of granulation. For instance, Japanese Un-Examined Patent Publication No. Hei 6-113749 discloses a method for fluidized bed-granulation, which comprises the step of granulating raw soybean protein powder while spraying the raw soybean protein powder with water or a water-containing liquid comprising, as a surfactant, a glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol and/or sucrose fatty acid ester. This method permits the improvement of the dispersibility of the resulting soybean protein powder, but does not solve the problems concerning the smell of soybean and taste. In addition, if the added amount of such a surfactant increases, the surfactant may adversely affect the taste of the resulting product.
Japanese Un-Examined Patent Publication No. Hei 9-215486 (BASIC EP 78437A) discloses a method for preparing a granular food comprising the steps of mixing a powdery raw material rich in carbohydrate and/or proteins with fats and oils or fats, further mixing the resulting mixture with a powdery raw material rich in carbohydrate and/or proteins to give a powdery and/or dough-like mixture, which preferably comprises, as expressed in terms of part by weight, 5 to 95 parts of carbohydrate, up to 40 parts of proteins and up to 80 parts of oils or fats, and then converting the mixture into granules with supplemental use of steam and/or an aqueous solution of maltodextrin, gum or starch. The product prepared by this method has a high content of components other than proteins and the method is not particularly developed for the granulation of soybean proteins.
As has been discussed above, the soybean protein products prepared according to the foregoing methods are insufficient for use as protein-supply foods and there is still room for improvement.
Japanese Un-Examined Patent Publication No. Hei 6-166622 discloses a food obtained by preferably incorporating hardly digestible dextrin into a food having a high content of sugar or a sugar-containing preparation granulated using hardly digestible dextrin. This patent also discloses that the sugar-containing preparation comprising the hardly digestible dextrin is effective for preventing obesity or abnormality of glucose tolerance and excellent in flowability and storability and therefore, it can easily be used in not only food industries, but also general families.